I agree that "please" and "thank you" are very useful; warmly recommended social lubricant or somesuch: with them, things just seem to work better.
I personally much prefer a followup report rather than a "thank you", though. A summary of what the OP did, whether the problem was solved, or ended up being sidestepped, and so on. Especially if the thread is then crawlable/possible to find via a web search, as then the overview is there to let others know how it went afterwards; kinda like listening to other people discuss how they solved a problem similar to one you happen to have right now. Useful, much better than a "book answer".
The way I write my answers is to target more than just the exact problem at hand, for a number of reasons.
One reason is that nobody ever describes their problem perfectly, so assuming the target is only approximately located makes for an easier discussion.
The other, the bigger one, is that it is usually not worthwhile to answer an obscure question by someone you don't know,
unless others can benefit from the question and answer as well.
Whenever I've helped people over email, I've always asked for the same thing: that someday, they pass the help on, and help someone else in turn. (You know,
pay it forward style.)
I do these, so that the original asker is just a participant in producing a solution to that particular class of problems that will be available later on, for everybody; and not in control of whether I feel my help was successful or not.
It's like helping build a community hall or something, emotion-wise. The act of
building something becomes the cause for the dopamine hit.
The downside is that you may get a similar affliction as I have, and see how much lasting damage people who know better but let their misunderstandings remain because they find it distasteful to admit being wrong ("hey, it's just one queastion, relax, who cares, it's not that bad").
(That is as annoying as trying to help someone who is being actively misled by a troller who tells the original asker to not listen to anybody else, and is leading them towards failure, often a delayed failure which will be a serious setback to the asker. Frustrating, like seeing too much sand being mixed in concrete, and a "contractor" assuring everyone it's okay because they have twenty years of experience, and you yourself are just a hobbyist but have happened to see how exactly that kind of mix leads to crumbling concrete, a real hazard, and a building that will be condemned. The waste of resources, the garbage being spewed out...)